This disclosure relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an example described below, more particularly provides well tools utilizing swellable materials which are activated on demand.
Swellable materials have been used in the past to perform various functions in well tools. For example, a swellable material may be used in a packer seal element to provide a packer assembly which is self-actuating downhole. When an appropriate fluid contacts the swellable material, the material swells and seals off an annulus in the well.
However, if the fluid is already present in the well, the swellable material can begin to swell as soon as it is installed in the well, which can lead to various problems. For example, the material could swell prematurely, which could prevent the packer assembly from being appropriately positioned in the well.
Techniques have been proposed for delaying the swelling of a swellable material but, in general, these techniques produce somewhat inaccurate delay times and can only be conveniently initiated at one time (e.g., when the swellable material is installed in the well). It has also been proposed to initiate swelling in response to application of pressure to an annulus surrounding the well tool, but if the well tool is used in an open hole, or in perforated or leaking casing, it may not be possible or convenient to apply pressure to the annulus.
Therefore, it will be appreciated that it would be desirable to provide improvements in the art of activating swellable materials in subterranean wells. Such improvements could be useful for initiating actuation of packer assemblies, as well as other types of well tools.